Method and apparatus for reducing particulate iron oxide to molten iron with solid reductant and oxy-fuel burners

ABSTRACT

A method and apparatus for reducing particulate iron oxide to molten iron utilizing solid carbonaceous fuel as reductant in a shaft type reducing furnace, in which a furnace burden is formed of a mixture of iron oxide lumps or pellets and particulate solid fuel. Reacted top gas is upgraded and recirculated through the burden in counterflow relationship thereby heating and reducing the burden. The heat for reduction is generated by passing electric current through the burden. A portion of the heat for melting of reduced iron and a supplemental source of hot reducing gas is provided by oxy-fuel burners located in the shaft furnace above the molten iron pool.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 892,564 filed Apr. 3, 1978, now U.S. Pat. No.4,179,278, which is a continuation-in-part application of U.S. patentapplication Ser. No. 769, 242, filed Feb. 16, 1977, now U.S. Pat. No.4,082,543.

BACKGROUND OF THE INVENTION

In recent years the direct reduction of iron oxide to metallic iron hasbecome a practical commercial reality with increasing worldwideacceptance and production. The direct reduced iron which results fromdirect reduction of iron oxide has a commercially demonstrated utilityin iron and steelmaking and particularly in electric arc furnacesteelmaking.

Direct reduced iron, which is sometimes known as sponge iron, is notsuited as the principal feed material for steelmaking furnaces otherthan electric arc furnaces. Other steelmaking processes such as thebasic oxygen process and the bottom blown oxygen process require largequantities of hot metal, or molten metal as feed material. Thus, foroxygen furnace feed, it is desired to produce a molten product from adirect reduction furnace.

A known type process gasifies solid fuel in a separate combustion-typegasifier utilizing oxygen and steam for gasification. The gas from thegasifier is then cooled and scrubbed, desulfurized, then utilized in adirect reduction furnace as the source of reductant. An example of thiscombination of gasifier and direct reduction furnace is described inU.S. Pat. No. 3,844,766. This combination also has a fundamental thermaldisadvantage in that approximately 50 percent of the solid fuel isconsumed by combustion in the gasifier and only the remaining 50 percentof the fuel value is available as a source of reductant. Thiscombination, although highly efficient in the use of the gas from thegasifier for reduction, requires approximately 4.0 to 5.0 Giga caloriesof solid fuel per metric ton of solid direct reduced iron product.

An electrically operated vertical shaft furnace is taught by U.S. Pat.No. 1,937,064 in which broken coke, graphite, silicon carbide or otherconductors are charged to form a burden. Molten metal is then pouredthrough the burden while electrical current also flows through theburden, thus refining the molten metal. The burden is a stationarygranular mass of carbonaceous material which does not flow through thefurnace. The burden also is not the material being treated, unlike thepresent invention.

Langhammer U.S. Pat. No. 3,894,864 purports to teach a shaft furnace forproducing molten steel by use of an electric arc. The patent fails toexplain the completion of the electric circuit which creates theelectric arc. Applicants distinguish from this process by utilizingdirect resistance heating of their burden, unlike any known reference,as well as by recirculating spent top gas to act as reductant source.

Other patents which may be of interest to the reader include Elvander etal U.S. Pat. No. 3,948,640 and Gross U.S. Pat. No. 3,948,642.

OBJECTS OF THE INVENTION

It is the principal object of the present invention to provide a methodfor directly reducing iron oxide to molten iron in a shaft typereduction furnace wherein solid fuel is utilized as the reductantsource.

It is another object of this invention to provide a method for directlyreducing iron oxide to molten iron in a shaft furnace wherein the energyinput requirements are greatly reduced over present commercial directreduction methods.

It is another object of this invention to provide means for moreefficient operation of a direct reduction shaft furnace than washeretofore possible.

It is another object of this invention to provide apparatus for carryingout the above methods.

SUMMARY OF THE INVENTION

The present invention is a direct reduction method utilizing solid fuelin a novel and highly thermally efficient manner wherein the solid fuelis consumed directly in the reduction process by reaction with oxygenprimarily from the iron oxide which is being reduced. The overallreactions in the furnace are endothermic, the heat required beingsupplied by electrically heating the burden. Minimizing the use of anexternal source of air or industrial oxygen for the carbon gasificationreactions results in a solid fuel requirement of approximately 2.3 Gigacalories per metric ton of direct reduced iron product with an electricenergy requirement of approximately 700 kwh (0.6 Giga calories) permetric ton of direct reduced iron in the solid state, with an additional0.33 Giga calories to further heat and melt the direct reduced iron andgangue provided by a combination of electric energy and the oxy-fuelburners.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be more readily understood by referring tothe following detailed specification and the appended drawings in which:

FIG. 1 is a schematic cross section of an elevational view of the shaftfurnace of the present invention and related equipment in which theelectric current flows parallel to the vertical axis of the furnace andthe energy for heating the direct reduced iron and gangue abovereduction temperature and melting it is supplied partially by electricenergy and partially by oxy-fuel burners.

FIG. 2 is a schematic cross section of an elevational view of analternative embodiment of the present invention in which the electriccurrent flows perpendicular to the vertical axis of the furnace and allthe energy for heating the direct reduced iron and gangue abovereduction temperature and melting it is supplied by the oxy-fuelburners.

DETAILED DESCRIPTION

Referring now to the embodiment of FIG. 1, a shaft type furnace 10having a steel shell 12 is lined with refractory 14. A feed hopper 16 ismounted at the top of furnace 10 for charging of particulate solids feedmaterial 18 therein. The feed material consists of iron oxide in theform of pellets or lumps, solid carbonaceous fuel and limestone. Thefeed material descends by gravity through one or more feed pipes 20 toform a packed bed 22 of particulate solids feed material or burden inthe furnace 10. Reduced molten product 23 is removed from the furnacethrough taphole 24. If desired, a slag taphole 26 can be provided at ahigher elevation. Removal of the molten iron and slag establishes agravitational flow of the particulate burden 22 through shaft furnace10.

The furnace 10 is preferably cylindrical but could have any desiredcross-section.

The upper region of the furnace is provided with at least one heatresistant alloy electrode 30, which extends through the steel furnaceshell 12 and across the furnace width. This electrode may be fixed orjournaled for rotation in bearings 32A and 32B which may be mountedexternally as shown, or insulated and mounted in the furnace walls 14.Each electrode rod may be equipped with one or more heat resistant alloydiscs 35 to provide an extended electrode surface area. The number ofelectrode rods employed is dependent upon the horizontal dimensions ofthe furnace. The bottom of the shaft furnace is a closed hearth linedwith carbon block 37, which enables the entire hearth to act as anelectrode. This carbon block hearth is connected to a source ofelectricity through electrode buss 38. Suitable thermocouples such as40A and 40B are inserted into the furnace through the refractory wall atselected elevations to assist in controlling the operation of theprocess.

Top gas exits the furnace through a top gas outlet pipe 44 located abovestockline 46. The lower end of feed pipe 20 extends below outlet pipe44, which arrangement creates a top gas disengaging plenum 48 whichpermits the top gas to exit generally symmetrically from the stockline46 and flow freely to the top gas outlet pipe 44.

A gas cleaning and recirculating circuit is provided to remove solidsand condensible matter from the top gas and to cool the gas to form coldprocess gas. The reacted top gas leaving the shaft furnace 10 throughpipe 44 flows to an oil scrubber 50 wherein tars, oils, and particulatesare removed from the gas as a sludge. Pump 52 pumps the sludge back tothe furnace either through pipe 53 to the oxy-fuel burners describedlater or through pipe 54 then through sludge injection pipe 56 which hasan open lower end extending well beneath the stockline 46 to insurereaction of sludge components with the burden and to prevent top gasfrom recycling these components back into the oil scrubber.

The top gas passes from the oil scrubber 50 to a water scrubber 60wherein the gas is further cooled and cleaned. A gas recirculatingblower 62 draws the cooled and cleaned process gas from the scrubber 60.A portion of the process gas is introduced to pipe 68 to assist ininjecting the sludge into the shaft furnace. Some process gas mustnormally be vented because when solid carbon in the furnace reacts withoxygen from the iron oxide, carbon monoxide gas and carbon dioxide gasare formed. Since this reaction involves a gaseous expansion, excess gasmay be vented through vent V1. Of course, this excess gas provides asource of energy for use elsewhere.

A second portion of the process gas passes through pipe 72 into gaspreheater 74 wherein the gas is heated to reducing temperature of about900° to 1000° C. The heated gas flows through pipe 76 and is introducedto the furnace through hot process gas inlet 78 and bustle 80. Anotherportion of the process gas is fed into pipe 86 as fuel for preheaterburner 90. Combustion air for the burner 90 is provided by air source92.

A multiplicity of oxy-fuel burners 94, two of which are shown, arepositioned peripherally in the lower region of furnace 10 below processgas inlet bustle 80 and above the pool of molten iron 23. The burners 94may be fired with the sludge removed from oil scrubber 50 and conveyedwith pump 52 through pipe 53 utilizing process gas from pipe 68 and pipe95 to assist in conveying, or they may be fired by any external fuelfrom source 96 such as pulverized coal, oil, tar, or natural gas. Aportion of the process gas may be introduced through line 95 to assistin conveying the external fuel from source 96 to the burner if required.The external fuel 96 or sludge injected through pipe 53 will be burnedwith a less than stoichiometric quantity of oxygen from an externalsource 98 to produce a flue gas that has a sufficient excess of thereductants CO+H₂ relative to the oxidants CO₂ +H₂ O to be reduced toiron oxide. This flue gas will flow upwardly through the furnace 10 andwill exit through outlet pipe 44. The oxy-fuel burners 94 will alsosupply a portion of the heat required to melt the reduced iron andassociated slag.

One or more electrodes 30 are provided, depending upon the dimensions ofthe horizontal cross-section of the furnace. The electrode acts as afeeder mechanism as well as a cluster breaker for material in the upperzone of the furnace. Each electrode can carry one or more radiallyextending breaker segments 35 and can be connected to and driven byoscillatible drive mechanism 100. Each cluster breaker segmentpreferably extends only about 180 to 270 degrees about the electrode,but alternatively it may extend completely around the electrode. Thus,as the electrode oscillates within the bearings, it acts as both a feedmechanism and cluster breaker mechanism. It feeds material alternatelyby moving material downwardly from opposite walls of the furnace whilesimultaneously breaking any clusters of the hot cohesive material.

In the method of this invention, iron oxide pellets, lump ore or othersuitable iron oxide feed material is mixed with limestone and solidcarbonaceous fuel such as coal, coke, or lignite, then fed through feedpipe 20 to the interior of the furnace 10 to form burden 22 therein as apacked bed.

The major portion of the furnace heat is supplied electro-thermally bypassing electric current through the burden between the hearth electrode37 and the upper alloy electrode 30 in the furnace. Directly reducediron pellets or lumps are electrically conductive even at the earlieststate of reduction when metallic iron is formed only on the pelletsurface. When starting up operation of the electric powered shaftfurnace of the present invention, the furnace is charged with reduced orpartially metallized directly reduced iron pellets, petroleum coke orany other electrically conductive material. Other conductive materialsare utilized when reduced or partially metallized pellets areunavailable. It has been determined that pellets with metallizations aslow as 6 percent are conductive.

An alternative embodiment of the invention depicted in FIG. 2 utilizesopposing pairs of electrode plates 103 to supply the electric energyrequirement for the reduction reaction and utilizes oxy-fuel burners 94to supply all the additional energy to further heat and melt the directreduced iron and gangue.

The furnace 110 of this embodiment is preferably square or rectangular,or has curvilinear sides which approach a square or rectangle when seenin horizontal cross section. The middle region of the furnace isprovided with heat resistant alloy electrode plates 103 connected toelectrode lead rods 112, which are in turn connected to an electricpower source not shown. Electrode plates 103 are preferably recessedinto the refractory wall 114 to create a substantially smooth interiorwall face. The electrode plates are so positioned to form opposingpairs. Three opposing pairs of electrode plates are shown in FIG. 2,vertically spaced through the furnace for reasons of process control.The electrode lead rods 112 are mounted on suitable electricalinsulating material 116 such as asbestos board which serves to insulatethe rod 112 from the steel furnace shell 118. A heat resistant alloypipe 120 having a closed lower end extends vertically through thefurnace roof and into the burden as far as the region of the lower-mostpair of electrode plates 103. Suitable thermocouples, not shown, areinserted into the thermocouple pipe 120 to sense the temperature of theburden at selected elevations, particularly at the elevation of eachpair of electrode plates.

The shaft furnace includes three distinct process zones. The upperregion constitutes a prereduction zone in which the burden is heated byconvection of gases moving in counterflow relation to the flow of theburden. Coal or other carbonaceous fuel in the feed liberatescondensible and noncondensible volatiles. The noncondensible volatiles,which are mostly hydrogen or hydrocarbons, exit as top gas, then arecleaned and recirculated as process gas. The pellet burden acts as amoving packed bed pebble quench which is very effective in preventingheavy liquid compounds from plugging gas outlet pipes. Some heavy oilsand tars tend to weep out of the coal and are absorbed by the oxide feedto subsequently react with CO₂ and water vapor in the process gas. Ahigh ratio of oxide feed to heavy liquid compounds reduces the tendencyof the burden to cluster excessively near the burden stockline. In thisprereduction zone, the oxide feed material is reduced to lowmetallization, i.e. metallization less than 25 percent, by reaction withreductants H₂ and CO in the upwardly moving gases. Thus the burdenbecomes electrically conductive before it leaves the prereduction zone.

The central region of the shaft furnace constitutes a reduction zone inwhich metallic iron is formed by reaction with the char formed from thereaction of the carbonaceous fuel with oxygen from the iron oxide. Thereactions in the reduction zone are endothermic. The required heat inthe reduction zone is supplied electrothermally. This heat requirementis approximately 700 kWh (0.6 Giga calories) per metric ton of directreduced iron. Excess heat in the reducing zone will cause the pellets tosoften and the burden to become a pasty mass which will tend to preventupflow of process gas through the burden, or to curtail upflow ofreducing gas. The circulation of the process gas from bustle 80 throughthe burden will help in maintaining the burden in solid particulate formuntil it reaches the melting zone.

The lower region of the furnace constitutes a melting zone wherein thehot reduced pellets are melted prior to discharge. The additional heatrequirement to melt the pellets is about 0.33 Giga calories per metricton. In FIG. 1 this heat is supplied in part by electrothermal heatingand in part by the oxy-fuel burners. In FIG. 2 this heat is suppliedentirely by the oxy-fuel burners 94. These burners enable the reducedpellets to be heated above the reducing temperature and to be meltedindependent of the electrical power requirement in the reduction zone.These burners also supply a hot reducing gas which decreases the powerrequirement for the reduction zone and the solid carbonceous fuelrequirement in the furnace feed.

The product discharge from the shaft furnace is molten iron with about 3to 12 percent impurities. The iron may be converted to steel in anoxygen steelmaking furnace, or it can be used as pig iron.

The coal in the feed material may range from about 5 to about 20 percentby weight of the charge, depending on the heating values of the coalselected.

A small amount, up to about 5 weight percent, of limestone or dolomiteor a mixture thereof may be added to the feed material to react withsulfur which may be liberated within the furnace. This nonmetallicmaterial can be separated from the molten iron product as slag organgue. An additional amount of limestone or dolomite is added to thefeed to fluidize the slag in accordance with normal slagging practice.

As a specific example of the operation of the furnace, calculations havebeen made regarding the gas flow rates, gas temperatures and gascompositions at a number of locations in the process flow diagram asdepicted in the drawings. These calculations have been based on an oxidefeed analysis of 97 percent Fe₂ O₃, with 3 percent gangue materials. 10percent more coal than is theoretically required, having a proximateanalysis of 50.1 percent fixed carbon, 3.8 percent water, 37.0 percentvolatiles and 9.1 percent ash was used as a basis for thesecalculations. This is a high volatile grade B bituminous coal. The samecoal is used as fuel for the oxy-fuel burners. The tar and oil yieldfrom the coal is about 0.17 cubic meters per metric ton. Tars and oilpresent in the top gas are 33,600 milligrams per normal cubic meter. Thetemperature in the reducing zone is 980° C. The metallization of theultimate product is 92 percent with the metallization taking place inthe prereduction zone being 20 percent. The use of excess coal willresult in carburizing the iron product.

Tables 1 and 2 show computed operating figures for a direct reductionfurnace operated in accordance with the invention. The gas analyses aretypical operating figures at the locations indicated by the letterheadings. These locations are as follows:

A. Top gas upon exit from top gas outlet 44.

B. Gas exiting water scrubber 60.

C. Gas passing through vent V1.

D. Gas entering furnace inlet 78.

E. Gas admitted to burner 90 from line 86.

F. Gas from oxy-fuel burner 94 at point of mixture with gas from furnaceinlet 78.

G. Gas mixture into the reduction zone.

H. Gas mixture out of the reduction zone.

I. Oxygen being admitted to burner 94 from source 98.

Gas flows in the tables are given in normal cubic meters per metric ton(Nm³ /t) of product.

Table 1 shows the operating figures for a direct reduction furnace beingoperated in accordance with FIG. 1 where 50% of the energy required toheat the direct reduced iron and gangue above reduction temperature andto melt it is supplied by the oxy-fuel burner.

                                      TABLE 1                                     __________________________________________________________________________                 A  B  C  D  E  F  G  H  I                                        __________________________________________________________________________    Flow- (Nm.sup.3 t Prod)                                                                    1440                                                                             1405                                                                             480                                                                              684                                                                              241                                                                              182                                                                              866                                                                              1410                                                                             69                                       Temp. -                                                                             (°C.)                                                                         299                                                                              43 43 982                                                                              43 982                                                                              982                                                                              982                                                                              25                                       Analysis -                                                                          %CO    46.7                                                                             47.9                                                                             47.9                                                                             52.0                                                                             47.9                                                                             54.8                                                                             52.5                                                                             62.6                                                                             --                                             %CO.sub.2                                                                            22.4                                                                             23.0                                                                             23.0                                                                             18.9                                                                             23.0                                                                             11.4                                                                             17.3                                                                             7.7                                                                              --                                             %H.sub.2                                                                             20.5                                                                             21.0                                                                             21.0                                                                             16.9                                                                             21.0                                                                             24.2                                                                             18.5                                                                             23.3                                                                             --                                             %H.sub.2 O                                                                           8.3                                                                              6.0                                                                              6.0                                                                              10.1                                                                             6.0                                                                              8.3                                                                              9.7                                                                              4.9                                                                              --                                             %CH.sub.4                                                                            1.6                                                                              1.6                                                                              1.6                                                                              1.6                                                                              1.6                                                                              0.3                                                                              1.4                                                                              1.0                                                                              --                                             %N.sub.2                                                                             0.5                                                                              0.5                                                                              0.5                                                                              0.5                                                                              0.5                                                                              1.0                                                                              0.6                                                                              0.5                                                                              2                                              %O.sub.2                                                                             -- -- -- -- -- -- -- -- 98                                       __________________________________________________________________________

Table 2 shows the operating figures for a direct reduction furnace beingoperated in accordance with the invention with the apparatus depicted inFIG. 2.

                                      TABLE 2                                     __________________________________________________________________________                 A  B  C  D  E  F  G  H  I                                        __________________________________________________________________________    Flow -                                                                              (Nm.sup.3 /t Prod)                                                                   1445                                                                             1408                                                                             633                                                                              527                                                                              248                                                                              364                                                                              892                                                                              1416                                                                             138                                      Temp -                                                                              (°C.)                                                                         306                                                                              43 43 982                                                                              43 982                                                                              982                                                                              982                                                                              25                                       Analysis -                                                                          %CO    46.2                                                                             47.4                                                                             47.4                                                                             51.7                                                                             47.4                                                                             54.8                                                                             53.0                                                                             61.9                                                                             --                                             %CO.sub.2                                                                            22.2                                                                             22.8                                                                             22.8                                                                             18.5                                                                             22.8                                                                             11.4                                                                             15.6                                                                             7.6                                                                              --                                             %H.sub.2                                                                             21.0                                                                             21.5                                                                             21.5                                                                             17.3                                                                             21.5                                                                             24.2                                                                             20.1                                                                             23.9                                                                             --                                             %H.sub.2 O                                                                           8.4                                                                              6.0                                                                              6.0                                                                              10.2                                                                             6.0                                                                              8.3                                                                              9.4                                                                              5.0                                                                              --                                             %CH.sub.4                                                                            1.6                                                                              1.7                                                                              1.7                                                                              1.7                                                                              1.7                                                                              0.3                                                                              1.1                                                                              1.0                                                                              --                                             %N.sub.2                                                                             0.6                                                                              0.6                                                                              0.6                                                                              0.6                                                                              0.6                                                                              1.0                                                                              0.8                                                                              0.6                                                                              2                                              %O.sub.2                                                                             -- -- -- -- -- -- -- -- 98                                       __________________________________________________________________________

Tests have been conducted to determine the electrical resistance atvarious temperatures of a packed bed burden consisting of 89 percentnominal 12 mm diameter pellets of approximately 90 percentmetallization, 10 percent nominal 12 mm diameter coal char from lowvolatile bituminous coal and 1 percent limestone of nominal 6 mmdiameter. In Table 3 the resistivity represents the resistance through aburden having a face area one meter square and a resistance path depthof one meter. The table represents points taken from a curve of plotteddata points:

                  TABLE 3                                                         ______________________________________                                                         Resistivity in                                               Temperature      Ohm-Meters                                                   ______________________________________                                        100° C.   .0055                                                        300° C.   .0033                                                        500° C.   .0020                                                        700° C.   .0012                                                        900° C.   .0007                                                        ______________________________________                                    

The preferred reduction temperature in the furnace of the presentinvention is in the range of 900° to 1000° C. The burden resistivity inthis temperature range at either low or high metallizations requiresrelatively high current at relatively low voltage which makes practicalthe resistance heating of the burden without need for sophisticatedelectrical insulation or grounding means.

The process of either FIG. 1 or FIG. 2 can be operated without a bustlegas preheater 74 by closing the valve in pipe 72. In this case, a largepercentage of the gas entering the reduction zone through inlet 78 iscold which will reduce the average temperature of the solid particlesleaving the reduction zone. Therefore additonal heat must be suppliedthrough the oxy fuel burners 94 to raise the temperature of the solidparticles to melting temperature. Additional electric energy is alsorequired to raise the temperature of the cold bustle gas to reactiontemperature in the reducing zone of the furnace.

Table 4 compares the furnace energy requirements when bustle gaspreheater 74 is used in the furnaces of both FIG. 1 and FIG. 2 and whenthe bustle gas preheater is bypassed.

                  TABLE 4                                                         ______________________________________                                        FURNACE ENERGY REQUIREMENTS                                                        ELEC-   PRO-                      % OF                                        TRIC    CESS    BURNER            MELTING                                     EN-     COAL    COAL    BUSTLE    HEAT                                        ERGY    Gcal/t  Gcal/t  GAS       FROM                                   FIG. kWh/t   (HHV)   (HHV)   PREHEATER BURNERS                                ______________________________________                                        1    893     2.38    0.67    YES        50%                                   2    672     2.31    1.34    YES       100%                                   1    1162    2.35    0.95    NO         50%                                   2    914     2.28    1.74    NO        100%                                   ______________________________________                                    

Table 5 shows the operating figures for a direct reduction furnace beingoperated in accordance with FIG. 1 without using bustle gas preheater74.

                                      TABLE 5                                     __________________________________________________________________________              A    B    C   D   E F   G   H    I                                  __________________________________________________________________________    Flow-(Nm.sup.3 /t Prod)                                                                 1442 1407 787 620 0 258 878 1413 98                                 Temp. - (°C.)                                                                    302  43   43  43  --                                                                              982 316 982  25                                 Analysis - %CO                                                                          46.6 47.7 47.7                                                                              47.7                                                                              --                                                                              54.8                                                                              52.6                                                                              62.3 --                                 %CO.sub.2 22.3 22.9 22.9                                                                              22.9                                                                              --                                                                              11.4                                                                              16.6                                                                              7.7  --                                 %H.sub.2  20.7 21.2 21.2                                                                              21.2                                                                              --                                                                              24.2                                                                              19.2                                                                              23.6 --                                 %H.sub.2 O                                                                              8.3  6.0  6.0 6.0 --                                                                              8.3 9.6 4.9  --                                 %CH.sub.4 1.6  1.7  1.7 1.7 --                                                                              0.3 1.3 1.0  --                                 %N.sub.2  0.5  0.5  0.5 0.5 --                                                                              1.0 0.7 0.5  2                                  %O.sub.2  --   --   --  --  --                                                                              --  --  --   98                                 __________________________________________________________________________

Table 6 shows the operating figures for a direct reduction furnace beingoperated without a bustle gas preheater 74 but in all other aspects inaccordance with the invention as depicted in FIG. 2 where nearly 100% ofthe energy required to heat the direct reduced iron gangue abovereduction temperature and to melt it is supplied by the oxy fuel burner94.

                                      TABLE 6                                     __________________________________________________________________________              A    B    C   D   E F   G   H    I                                  __________________________________________________________________________    Flow - (nm.sup.3 /t Prod)                                                               1447 1409 977 432 0 473 905 1419 180                                Temp. - (°C.)                                                                    309  43   43  43  --                                                                              982 538 982  25                                 Analysis - %CO                                                                          46.0 47.2 47.2                                                                              47.2                                                                              --                                                                              54.8                                                                              53.3                                                                              61.7 --                                 %CO.sub.2 22.1 22.7 22.7                                                                              22.7                                                                              --                                                                              11.4                                                                              14.7                                                                              7.6  --                                 %H.sub.2  21.2 21.8 21.8                                                                              21.8                                                                              --                                                                              24.2                                                                              21.0                                                                              24.1 --                                 %H.sub.2 O                                                                              8.5  6.0  6.0 6.0 --                                                                              8.3 9.2 5.0  --                                 %CH.sub.4 1.6  1.7  1.7 1.7 --                                                                              0.3 1.0 1.0  --                                 %N.sub.2  0.6  0.6  0.6 0.6 --                                                                              1.0 0.8 0.6  2                                  %O.sub.2  --   --   --  --  --                                                                              --  --  --   98                                 __________________________________________________________________________

SUMMARY OF THE ACHIEVEMENTS OF THE OBJECTS OF THE INVENTION

It is clear from the above that we have invented a method and apparatusfor directly reducing iron oxide to molten iron in a shaft typereduction furnace utilizing solid fuel as the reductant source in whichenergy input requirements are greatly reduced over present commercialdirect reduction plants and with more efficient operation than wastheretofore possible.

It is understood that the foregoing description and specific examplesare merely illustrative of the principles of the invention and thatvarious modifications and additions may be made thereto by those skilledin the art without departing from the spirit and scope of the inventionas set forth in the appended claims.

What is claimed is:
 1. Apparatus for reducing particulate iron oxide tomolten iron with a solid reductant, said apparatus comprising:a. agenerally vertical shaft furnace having a particle introducing means atthe top thereof for establishing a gravitationally descending burdentherein, a molten iron collection chamber at the bottom thereof, andmolten iron removal means; b. means for passing an electric currentthrough said burden by electric resistance heating, including anexterior source of electric power; c. a gas outlet in the upper regionof said furnace for removing top gas; d. means external to said furnacefor cooling and cleaning removed top gas, said cooling and cleaningmeans communicating with said means for removing top gas; e. meanscommunicating with said top gas cooling and cleaning means and with theinterior of said furnace above said molten iron collection chamber forintroducing said cooled and cleaned top gas to said furnace between saidgas outlet and said molten iron collection chamber; and f. at least oneoxy-fuel burner in said shaft furnace between said molten metalcollection chamber and said means for introducing cooled and cleaned topgas to said furnace, whereby said oxy-fuel burner provides heat formelting of reduced iron as well as a supplemental source of hot reducinggas.
 2. Apparatus according to claim 1 wherein said oxy-fuel burner isprovided with a source of oxygen and a source of fuel selected from thegroup comprising pulverized coal, oil, tar, natural gas, oil scrubbersludge, reacted top gas and combinations thereof.
 3. Apparatus accordingto claim 1 wherein said means for cooling and cleaning said removed topgas is a scrubber system comprising an oil scrubber followed by a waterscrubber.
 4. Apparatus according to claim 3 further comprising a sludgeinjection pipe in said furnace communicating with said oil scrubber forrecirculating oil scrubber sludge into said furnace.
 5. Apparatusaccording to claim 1 wherein said means for passing electric currentthrough said burden comprises a hearth electrode positioned in saidmolten iron collection chamber and at least one second electrodepositioned near the top of said furnace below the bottom of saidparticle introducing means.
 6. Apparatus according to claim 5 whereinsaid second electrode is journaled for rotation.
 7. Apparatus accordingto claim 5 wherein said second electrode is provided with at least oneheat resistant alloy disc.
 8. Apparatus according to claim 1 whereinsaid means for passing electric current through said burden compriseshorizontally opposed heat resistant electrode plates in the furnacewalls.
 9. Apparatus according to claim 1 further comprising meanscommunicating with said top gas cooling and cleaning means and with theinterior of said furnace for heating at least a portion of said cleanedand cooled top gas.